The present invention relates to electrical equipment such as a computer apparatus, and more specifically, to electrical equipment configured such that a power supply source such as an AC adapter and a battery which discharges after being charged are connectable thereto.
In various types of electrical equipment including information terminal equipment, represented by a notebook-type personal computer (notebook PC), personal equipment such as a PDA (Personal Digital Assistant), various types of portable audio equipment, a video camera, and the like, part of the time that the equipment receives a supply of power from a battery (a storage battery, a secondary battery or a battery) that is used over and over again while repeating charge and discharge, and a part of the time that the equipment receives power directly from a commercial power source through, for example, an AC adapter. A nickel hydrogen battery (NiMH battery) and a nickel cadmium battery, each of which has a relatively large capacity and is inexpensive, may be used as such a battery. Moreover, in some cases, the battery may be a lithium ion battery, in which energy density per unit weight is higher as compared with that of the nickel cadmium battery, a lithium polymer battery using solid polymer electrolyte instead of using liquid electrolyte, and the like.
Such electrical equipment, for example, the notebook PC, is sometimes configured such that both the AC adapter and the battery can be connected to a main body of a system thereof. In such a case, voltage of the AC adapter is higher as compared with voltage of the battery, and accordingly, power is supplied from the AC adapter to the system when both the AC adapter and the battery are connected thereto. In general, it is only in a case where the AC adapter is detached from the main body or a power supply path from the AC adapter is blocked by means of a switch or the like that the battery is used as a drive power source. Moreover, in a case where the AC adapter is connected to the main body, the battery is automatically charged by the AC adapter. For this reason, when the AC adapter is connected to the main body of the system, a large amount of power is constantly supplied thereto from the commercial power source.
Meanwhile, in recent years, “peak shift” has been studied to reduce peak power during a time such as a summer afternoon, when a demand for power is extremely large since power consumption rapidly increases due to, for example, use of air conditioners (for example, one o'clock through four o'clock during a daytime). Moreover, in Japan, a power expense at night is less expensive as compared with that in the daytime, and it has been requested to limit a supply of power from the commercial power source in the daytime.
For the subject described above, conventional technology exists which enables automatic switching between the AC drive and the battery drive in response to a time setting, thereby achieving effective utilization of power (for example, refer to Patent Document 1). Moreover, the applicants of the present invention have proposed a technology of optimizing power consumption. In this technology, together with a drive mode by the battery and a drive mode by the AC adapter, a dual mode of supplying power from both of the sources is provided as a power supply mode. Moreover, the invention allows selection of a source of power supplied to each subsystem depending on whether or not the battery can last until a shutdown time of stopping the supply of power from the AC adapter (for example, refer to Patent Document 2).
[Patent Document 1] Japanese Patent Laid-Open No. 2000-29576 (pp. 5-6, FIG. 2)
[Patent Document 2] Japanese Patent Laid-Open 2003-150281 (pp. 6-7, FIG. 2)
Moreover, for example, in the notebook PC, there is a power management function of limiting power consumption of the main body of the system. In a reduction operation of the power consumption by this power management function, for example, the operating speed of a CPU is reduced. One way to reduce operation speed of the CPU, for example, is so-called throttling, in which ON/OFF operation of the CPU is repeated to decrease apparent clock frequency. Another example of a way to reduce operating speed of the CPU is the Intel SpeedStep (registered trademark) Technology of the Intel Corporation, which is a technology of decreasing clock frequency of the CPU and the voltage supplied thereto. For example, when the notebook PC is driven by the battery, a power management for limiting discharge power is executed in order to prevent a temperature rise of a battery pack in which the battery is built.
Today, for example, there are notebook PCs installed with power-consuming, high-performance CPUs. At the same time, there are notebook PCs which support the peak shift function by utilizing technologies in the aforementioned Patent Documents 1 and 2. However, since each notebook PC is driven by a battery during the peak shift period, the aforementioned power management function limits the operation speed of the system to approximately, for example, 50% (lithium ion battery) or 37% (nickel hydrogen battery). Although portability is important in the notebook PCs, users use the notebook PCs in a similar manner to desktop PCs. Thus, the users naturally expect full-performance of the notebook PCs. However, in the case where the power management function works automatically, the operation speed of the CPU must be reduced upon power supply from a battery in the actual situation. This happens because, for example, the operation for reducing power consumption to prevent a temperature rise. Therefore, the notebook PCs do not sufficiently meet the demands of the users.